Color filters are used for liquid crystal displays (LCDs), optical filters for cameras, and the like. Color filters may be manufactured by coating a fine region colored with three or more colors on a charge coupled device or a transparent substrate. This colored thin film can be manufactured using various methods such as dyeing, printing, electrophoretic deposition (EPD), pigment dispersion, and the like.
The dyeing method forms a colored film by forming an image with a dyeing agent on a substrate, and then dyeing the image with direct dyes. Examples of the dyeing agent useful in the manufacture of colored thin films include natural photosensitive resins such as gelatin and the like, amine-modified polyvinyl alcohols, amine-modified acrylic-based resins, and the like. However, the dyeing process may be complex and lengthy, since it should include resist printing whenever a color needs to be changed to form a multi-colored thin film on the same substrate. In addition, many generally-used dyes and resins may have good color vividness and dispersion, but may also have poor color fastness, water resistance, and heat resistance, which are very important characteristics. For example, Korean Patent Nos. 1991-0004717 and 1994-0007778 include azo and azide compounds as a dye, which have deteriorated heat resistance and durability compared with a pigment.
The printing method forms a colored thin film by printing an ink prepared by dispersing a pigment into a thermally curable or photocurable resin and curing it with heat or light. This method may decrease material costs compared with other methods, but it is difficult to form a fine and precise image and acquire a uniform thin film layer. Korean Patent Laid-Open Publication Nos. 1995-7003746 and 1996-11513 disclose a method of making a color filter using an inkjet method. However, the resultant color filter suffers similar problems to a color filter made using dyeing techniques, such as deteriorated durability and heat resistance, because a dye-type color resist composition is also used and dispersed from a nozzle to accomplish fine and precise color printing in this inkjet printing method.
Korean Patent Laid-Open Publication Nos. 1993-7000858 and 1996-0029904 disclose electrophoretic deposition (EPD) in an electric precipitation method. The electrophoretic deposition (EPD) may form a precise color film having excellent heat resistance and color fastness, since it uses a pigment. However, this method may not be applied to a highly precise color filter requiring a finer electrode pattern for a more precise pixel in the future, because it may produce a colored film that is stained or thicker at both ends due to electrical resistance.
The pigment dispersion method forms a colored film by repeating a series of processes such as coating, exposing to light, developing, and curing a photopolymer composition including a coloring agent on a transparent substrate including a light-blocking layer (black matrix). This method may improve heat resistance and durability, which are very important characteristics for a color filter, and may provide a uniform film thickness. For example, Korean Patent Laid-Open Publications No. 1992-7002502, Korean Patent Nos. 1994-0005617, and 1995-0011163, Korean Patent Laid-Open Publication No. 1995-7000359, and the like disclose a method of making a color resist in a pigment dispersion method.
In this pigment dispersion method, a photosensitive resin composition for a color filter generally includes a binder resin, a photopolymerization monomer, a photopolymerization initiator, an epoxy resin, a solvent, and other additives. For example, the binder resin may include a carboxyl-containing acrylic-based copolymer, as in Japanese Patent Laid-Open Publications Pyung 7-140654 and 10-254133.
In particular, color filters have recently been manufactured in a consecutive process for mass production. In addition, the color filters have been manufactured by using a coloring photosensitive resin composition having a pigment particle diameter for high quality, and accordingly, a photosensitive resin composition having a wide process margin is required. However, the coloring photosensitive resin composition can lower process yield, since a resist in a non-exposed region may not be completely removed during formation of a fine pattern for a color filter or a pattern can be unsatisfactorily formed, which requires a color photoresist having excellent development characteristics.